Discussion: when it comes to "slow" to heat up..some bizarre reason people must imagine letting their thermostat to drop to say 50F (10C)before turning it on and then see themselves standing there with a time clock to count how many hours it takes to heat the room up to comfort conditions. With one run of the mill strategy, as soon as the outdoor temperature drops below some preselected outdoor ambient temperature, say 65F (18C), an outdoor reset control wakes up from it's sleep mode and starts to monitor the interior and exterior conditions and wakes up the boiler controls..it continues to get cold outside and it shows up inside as drop in temperature - then it starts to manage the system fluid and heater by turning it on and ramping up the fluid temperature.
With a well designed system with proper controls you can maintain comfort all the way from 65F (18C) outdoor conditions down to design conditions without having to "wait" for the system..is unless of course you actually enjoy starting up your system at polar temperatures.
Ive never understood these comments since ventilation is required regardless of what type of HVAC system you have.
Just because you have radiant doesnt make you exempt from building codes you still need to ventilateand that takes air.
Look at it this way; a characteristic of heat is temperature, it and moisture are measured with completely different instruments respectively a thermometer and a hygrometer.With proper designs and fabrication including passive and active controls there is marginal differences in thermal comfort between air and radiant based systems.For the range and rate of temperature changes acceptable to occupants see ASHRAE Standard 55 - Thermal Environmental Conditions for Human Occupancy.Also you dont need to move air for thermal comfort. Pipes aren't made of polyurethane nor are floor furnaces even close to underfloor radiant systems. Keep reading below for other amusing statements and claims. Here's what the ASHRAE Systems Handbook says, "A temperature controlled surface is called a radiant panel if 50% or more of the design heat transfer on the temperature-controlled surface takes place by thermal radiation." There are several "authoritative" sites on the internet which claim that radiant systems such as floors are not radiant systems at all, further they go on to state that these systems should be called convective systems.
We suspect the authors have confused "baseboard" systems with radiant systems where the former is predominately convection and the latter by ASHRAE definition a radiant system.
Describing radiant heat as dry would be like saying energy is dry.